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            <div><h4 class="title">
                <a name="asio.reference.async_read_until.overload11"></a><a class="link" href="overload11.html"
                                                                            title="async_read_until (11 of 12 overloads)">async_read_until
                (11 of 12 overloads)</a>
            </h4></div>
        </div>
    </div>
    <p>
        Start an asynchronous operation to read data into a dynamic buffer sequence
        until some part of its data matches a regular expression.
    </p>
    <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span>
    <span class="keyword">typename</span> <a class="link" href="../AsyncReadStream.html"
                                             title="Buffer-oriented asynchronous read stream requirements">AsyncReadStream</a><span
                class="special">,</span>
    <span class="keyword">typename</span> <a class="link" href="../DynamicBuffer_v2.html"
                                             title="Dynamic buffer requirements (version 2)">DynamicBuffer_v2</a><span
                class="special">,</span>
    <span class="keyword">typename</span> <a class="link" href="../ReadToken.html" title="Read token requirements">ReadToken</a> <span
                class="special">=</span> <a class="link"
                                            href="../asynchronous_operations.html#asio.reference.asynchronous_operations.default_completion_tokens"><span
                class="emphasis"><em>DEFAULT</em></span></a><span class="special">&gt;</span>
<a class="link"
   href="../asynchronous_operations.html#asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type"><span
        class="emphasis"><em>DEDUCED</em></span></a> <span class="identifier">async_read_until</span><span
                class="special">(</span>
    <span class="identifier">AsyncReadStream</span> <span class="special">&amp;</span> <span class="identifier">s</span><span
                class="special">,</span>
    <span class="identifier">DynamicBuffer_v2</span> <span class="identifier">buffers</span><span
                class="special">,</span>
    <span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span
                class="identifier">regex</span> <span class="special">&amp;</span> <span
                class="identifier">expr</span><span class="special">,</span>
    <span class="identifier">ReadToken</span> <span class="special">&amp;&amp;</span> <span
                class="identifier">token</span> <span class="special">=</span> <a class="link"
                                                                                  href="../asynchronous_operations.html#asio.reference.asynchronous_operations.default_completion_tokens"><span
                class="emphasis"><em>DEFAULT</em></span></a><span class="special">,</span>
    <span class="keyword">typename</span> <span class="identifier">constraint</span><span
                class="special">&lt;</span> <span class="identifier">is_dynamic_buffer_v2</span><span class="special">&lt;</span> <span
                class="identifier">DynamicBuffer_v2</span> <span class="special">&gt;::</span><span class="identifier">value</span> <span
                class="special">&gt;::</span><span class="identifier">type</span>  <span class="special">=</span> <span
                class="number">0</span><span class="special">);</span>
</pre>
    <p>
        This function is used to asynchronously read data into the specified dynamic
        buffer sequence until the dynamic buffer sequence's get area contains some
        data that matches a regular expression. It is an initiating function for
        an <a class="link" href="../../overview/model/async_ops.html" title="Asynchronous Operations">asynchronous
        operation</a>,
        and always returns immediately. The asynchronous operation will continue
        until one of the following conditions is true:
    </p>
    <div class="itemizedlist">
        <ul class="itemizedlist" type="disc">
            <li class="listitem">
                A substring of the dynamic buffer sequence's get area matches the regular
                expression.
            </li>
            <li class="listitem">
                An error occurred.
            </li>
        </ul>
    </div>
    <p>
        This operation is implemented in terms of zero or more calls to the stream's
        async_read_some function, and is known as a <span class="emphasis"><em>composed operation</em></span>.
        If the dynamic buffer sequence's get area already contains data that matches
        the regular expression, this asynchronous operation completes immediately.
        The program must ensure that the stream performs no other read operations
        (such as async_read, async_read_until, the stream's async_read_some function,
        or any other composed operations that perform reads) until this operation
        completes.
    </p>
    <h6>
        <a name="asio.reference.async_read_until.overload11.h0"></a>
        <span><a name="asio.reference.async_read_until.overload11.parameters"></a></span><a class="link"
                                                                                            href="overload11.html#asio.reference.async_read_until.overload11.parameters">Parameters</a>
    </h6>
    <div class="variablelist">
        <p class="title"><b></b></p>
        <dl>
            <dt><span class="term">s</span></dt>
            <dd><p>
                The stream from which the data is to be read. The type must support
                the AsyncReadStream concept.
            </p></dd>
            <dt><span class="term">buffers</span></dt>
            <dd><p>
                The dynamic buffer sequence into which the data will be read. Although
                the buffers object may be copied as necessary, ownership of the underlying
                memory blocks is retained by the caller, which must guarantee that
                they remain valid until the completion handler is called.
            </p></dd>
            <dt><span class="term">expr</span></dt>
            <dd><p>
                The regular expression.
            </p></dd>
            <dt><span class="term">token</span></dt>
            <dd>
                <p>
                    The <a class="link" href="../../overview/model/completion_tokens.html" title="Completion Tokens">completion
                    token</a> that will be used to produce a completion handler, which
                    will be called when the read completes. Potential completion tokens
                    include <a class="link" href="../use_future.html" title="use_future"><code
                        class="computeroutput"><span class="identifier">use_future</span></code></a>,
                    <a class="link" href="../use_awaitable.html" title="use_awaitable"><code
                            class="computeroutput"><span class="identifier">use_awaitable</span></code></a>,
                    <a class="link" href="../yield_context.html" title="yield_context"><code
                            class="computeroutput"><span class="identifier">yield_context</span></code></a>,
                    or a function object with the correct completion signature. The function
                    signature of the completion handler must be:
                </p>
                <pre class="programlisting"><span class="keyword">void</span> <span
                        class="identifier">handler</span><span class="special">(</span>
  <span class="comment">// Result of operation.</span>
  <span class="keyword">const</span> <span class="identifier">asio</span><span class="special">::</span><span
                            class="identifier">error_code</span><span class="special">&amp;</span> <span
                            class="identifier">error</span><span class="special">,</span>

  <span class="comment">// The number of bytes in the dynamic buffer</span>
  <span class="comment">// sequence's get area up to and including the</span>
  <span class="comment">// substring that matches the regular expression.</span>
  <span class="comment">// 0 if an error occurred.</span>
  <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span
                            class="identifier">bytes_transferred</span>
<span class="special">);</span>
</pre>
                <p>
                    Regardless of whether the asynchronous operation completes immediately
                    or not, the completion handler will not be invoked from within this
                    function. On immediate completion, invocation of the handler will
                    be performed in a manner equivalent to using <a class="link" href="../post.html" title="post"><code
                        class="computeroutput"><span class="identifier">post</span></code></a>.
                </p>
            </dd>
        </dl>
    </div>
    <h6>
        <a name="asio.reference.async_read_until.overload11.h1"></a>
        <span><a name="asio.reference.async_read_until.overload11.completion_signature"></a></span><a class="link"
                                                                                                      href="overload11.html#asio.reference.async_read_until.overload11.completion_signature">Completion
        Signature</a>
    </h6>
    <pre class="programlisting"><span class="keyword">void</span><span class="special">(</span><span class="identifier">asio</span><span
            class="special">::</span><span class="identifier">error_code</span><span class="special">,</span> <span
            class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span
            class="special">)</span>
</pre>
    <h6>
        <a name="asio.reference.async_read_until.overload11.h2"></a>
        <span><a name="asio.reference.async_read_until.overload11.remarks"></a></span><a class="link"
                                                                                         href="overload11.html#asio.reference.async_read_until.overload11.remarks">Remarks</a>
    </h6>
    <p>
        After a successful async_read_until operation, the dynamic buffer sequence
        may contain additional data beyond that which matched the regular expression.
        An application will typically leave that data in the dynamic buffer sequence
        for a subsequent async_read_until operation to examine.
    </p>
    <h6>
        <a name="asio.reference.async_read_until.overload11.h3"></a>
        <span><a name="asio.reference.async_read_until.overload11.example"></a></span><a class="link"
                                                                                         href="overload11.html#asio.reference.async_read_until.overload11.example">Example</a>
    </h6>
    <p>
        To asynchronously read data into a <code class="computeroutput"><span class="identifier">std</span><span
            class="special">::</span><span class="identifier">string</span></code>
        until a CR-LF sequence is encountered:
    </p>
    <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span
            class="identifier">string</span> <span class="identifier">data</span><span class="special">;</span>
<span class="special">...</span>
<span class="keyword">void</span> <span class="identifier">handler</span><span class="special">(</span><span
                class="keyword">const</span> <span class="identifier">asio</span><span class="special">::</span><span
                class="identifier">error_code</span><span class="special">&amp;</span> <span class="identifier">e</span><span
                class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span
                class="identifier">size_t</span> <span class="identifier">size</span><span class="special">)</span>
<span class="special">{</span>
  <span class="keyword">if</span> <span class="special">(!</span><span class="identifier">e</span><span class="special">)</span>
  <span class="special">{</span>
    <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span
                class="identifier">line</span> <span class="special">=</span> <span class="identifier">data</span><span
                class="special">.</span><span class="identifier">substr</span><span class="special">(</span><span
                class="number">0</span><span class="special">,</span> <span class="identifier">n</span><span
                class="special">);</span>
    <span class="identifier">data</span><span class="special">.</span><span class="identifier">erase</span><span
                class="special">(</span><span class="number">0</span><span class="special">,</span> <span
                class="identifier">n</span><span class="special">);</span>
    <span class="special">...</span>
  <span class="special">}</span>
<span class="special">}</span>
<span class="special">...</span>
<span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_read_until</span><span
                class="special">(</span><span class="identifier">s</span><span class="special">,</span> <span
                class="identifier">data</span><span class="special">,</span>
    <span class="identifier">boost</span><span class="special">::</span><span class="identifier">regex</span><span
                class="special">(</span><span class="string">"\r\n"</span><span class="special">),</span> <span
                class="identifier">handler</span><span class="special">);</span>
</pre>
    <p>
        After the <code class="computeroutput"><span class="identifier">async_read_until</span></code>
        operation completes successfully, the string <code class="computeroutput"><span
            class="identifier">data</span></code>
        contains the data which matched the regular expression:
    </p>
    <pre class="programlisting"><span class="special">{</span> <span class="char">'a'</span><span
            class="special">,</span> <span class="char">'b'</span><span class="special">,</span> <span class="special">...,</span> <span
            class="char">'c'</span><span class="special">,</span> <span class="char">'\r'</span><span
            class="special">,</span> <span class="char">'\n'</span><span class="special">,</span> <span
            class="char">'d'</span><span class="special">,</span> <span class="char">'e'</span><span
            class="special">,</span> <span class="special">...</span> <span class="special">}</span>
</pre>
    <p>
        The call to <code class="computeroutput"><span class="identifier">substr</span></code> then
        extracts the data up to and including the match, so that the string <code class="computeroutput"><span
            class="identifier">line</span></code> contains:
    </p>
    <pre class="programlisting"><span class="special">{</span> <span class="char">'a'</span><span
            class="special">,</span> <span class="char">'b'</span><span class="special">,</span> <span class="special">...,</span> <span
            class="char">'c'</span><span class="special">,</span> <span class="char">'\r'</span><span
            class="special">,</span> <span class="char">'\n'</span> <span class="special">}</span>
</pre>
    <p>
        After the call to <code class="computeroutput"><span class="identifier">erase</span></code>,
        the remaining data is left in the string <code class="computeroutput"><span
            class="identifier">data</span></code>
        as follows:
    </p>
    <pre class="programlisting"><span class="special">{</span> <span class="char">'d'</span><span
            class="special">,</span> <span class="char">'e'</span><span class="special">,</span> <span class="special">...</span> <span
            class="special">}</span>
</pre>
    <p>
        This data may be the start of a new line, to be extracted by a subsequent
        <code class="computeroutput"><span class="identifier">async_read_until</span></code> operation.
    </p>
    <h6>
        <a name="asio.reference.async_read_until.overload11.h4"></a>
        <span><a name="asio.reference.async_read_until.overload11.per_operation_cancellation"></a></span><a class="link"
                                                                                                            href="overload11.html#asio.reference.async_read_until.overload11.per_operation_cancellation">Per-Operation
        Cancellation</a>
    </h6>
    <p>
        This asynchronous operation supports cancellation for the following <a class="link"
                                                                               href="../cancellation_type.html"
                                                                               title="cancellation_type"><code
            class="computeroutput"><span class="identifier">cancellation_type</span></code></a>
        values:
    </p>
    <div class="itemizedlist">
        <ul class="itemizedlist" type="disc">
            <li class="listitem">
                <code class="computeroutput"><span class="identifier">cancellation_type</span><span
                        class="special">::</span><span class="identifier">terminal</span></code>
            </li>
            <li class="listitem">
                <code class="computeroutput"><span class="identifier">cancellation_type</span><span
                        class="special">::</span><span class="identifier">partial</span></code>
            </li>
        </ul>
    </div>
    <p>
        if they are also supported by the <code class="computeroutput"><span
            class="identifier">AsyncReadStream</span></code>
        type's <code class="computeroutput"><span class="identifier">async_read_some</span></code>
        operation.
    </p>
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            <div class="copyright-footer">Copyright © 2003-2022 Christopher M. Kohlhoff<p>
                Distributed under the Boost Software License, Version 1.0. (See accompanying
                file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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